Insular Italy occupies one-sixth of the national territory in surface area. Territorially, both Sicily and Sardinia include several minor islands and archipelagoes administratively dependent on the mother islands.

Sicily is the largest island in the Mediterranean (25,708 km²) and one of the largest of Europe, while Sardinia is only slightly less extensive (24,090 km²). The lowlands are generally limited in the geographic region and generally appear as narrow coastal belts. The only exceptions are the Campidano and Nurra in Sardinia and the Plain of Catania in Sicily that extend 1200 km² and 430 km² respectively. The rest of the area is prevalently hilly, with hills occupying 70% of the territory. Sicily is home to Mount Etna, Italy's highest non-Alpine peak and Europe's largest active volcano. Sardinia is home to the Gennargentu mountain range.

The population of Insular Italy totals a combined 6.7 million residents. Insular Italy has a population density of less than half the national average due to the scarce population of Sardinia, one of the least densely populated regions of Italy; Sicily, meanwhile, has a population density five times higher than Sardinia, however, the average results in Insular Italy having a low population density. Their combined populations total just one-tenth of the national population making Insular Italy the least populated macro-region of the country.

The following is a list of cities with a population of greater than 100,000 residents.

The unemployment rate of Sicily is the highest in the country at 11.9%, while in Sardinia between 2006-07 it dropped for the first time below 10%, reaching 8.6%, the lowest of all the Mezzogiorno regions, excluding Molise and Abruzzo. The low level of entrepreneurship in Sicily is tied to criminality, while in Sardinia it results from operating expenses (electricity, transportation, etc.) 20-50% higher than other regions due to its isolated location from the mainland: this handicap, in Sardinia, was reduced with the development of information technologies, like Tiscali, low-cost carrier, like Ryanair, and the territorial continuity (continuità territoriale) legislation about fares and routes between the islands and mainland Italy.